21721400081 has 4 divisors (see below), whose sum is σ = 21728598000. Its totient is φ = 21714202164.

The previous prime is 21721400053. The next prime is 21721400087. The reversal of 21721400081 is 18000412712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21721400081 - 2⁶ = 21721400017 is a prime.

It is a super-2 number, since 2×21721400081² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21721400081.

It is not an unprimeable number, because it can be changed into a prime (21721400087) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3594431 + ... + 3600468.

It is an arithmetic number, because the mean of its divisors is an integer number (5432149500).

Almost surely, 2^21721400081 is an apocalyptic number.

It is an amenable number.

21721400081 is a deficient number, since it is larger than the sum of its proper divisors (7197919).

21721400081 is an equidigital number, since it uses as much as digits as its factorization.

21721400081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7197918.

The product of its (nonzero) digits is 896, while the sum is 26.

Adding to 21721400081 its reverse (18000412712), we get a palindrome (39721812793).

The spelling of 21721400081 in words is "twenty-one billion, seven hundred twenty-one million, four hundred thousand, eighty-one".